- MAY 4 19?.7 O. N. I. Publication No. 45 Most Confidential! • . • . NA VY DEPARTM.ENT OFFICE OF NAVAL INTELLIGENCE OCTOBER, 1918 ) I - • WASHINGTON GOVERNMENT PRINTING OFFICE 1918 DF.f'L ~SI FiRe ~ A utll (lrll: C D lo s·t, I i __ _ _,, ____ I ----- __ ___!_ -~ DEPTH-CHARGE PROBLEMS. Lieu tenant Commander H. H . F ROST, United States Nai:y . In 0. N . I. Publicittion No. 44, " Gcrm1tn Submarine Attacks" i t wa!'; seen that Germans use four stnnd nrd torpedo shots: 1. D irect bow shot. 2. D irect s tern shot. :3_ 90° angled bow shot on parallel courses. 4. 90° angled s tern shot on opposite cow·scs. As in other pnrts of the subject of naval tactics it is neither possible nor desira.ble to lay down Jrnrd and fas t rules for the depth-ch a1-gc attack. A s tudy of a gren.t numher of actual s itua tions will r esult in th e deduction of several general principles regarding th e attack. Once these principles a.re nrnster ecl a dcpth-cha.r O'e doctrine can be_l aid _down. This c~n b_e followed in a m ajority of the :i c tua.l situations wh ich m ay b e cx;ected . I n some s1tua t1ons, how~ver, 1t will ~10t apply and th en the ('Ommn.nding o fliccr must fall h nck u pon his g encr n.l knowledge of th e suhJect and dcc1clc on the spot as to the b est m 0nsurcs to tn kc. I t would be il. trcmenclous undertaking to presen t all th e actunl situations wh ich mi0o-ht be r easonably nxpectcd in actual practice. The submarine, as we have seen, n1n .r fire i1 t least four stn ndm·d shots; i t m ay b e a l JB -hoat with a small t urning circle of 200 m eters, a U-boat with one of 400 meters, or a converted rner ­ MOST CONFIDENTIAL. can t~c s~bmarine with one of probn.hl_y 500 m eters. T he Yessel m aking t he clep th-ch a.rgc attack may have n. 10 NAVY DEPARTMENT, turnmg cll"cle of from 200 to 800 yards and a sp eed from to 30 knots. Tho s ubmarine m n._y attack from on the OFFICE OF NAVAL INTELLIGENCE bow, from on the be,1m, or from on tho qun.r ter. As this p ap er is prim ar ily written for the offi.cers of the A mcr­ ' ic~n P a trol D cbchmcnt, co~posctl of y ach ts, gunboR. ts, nncl cruisers, the vessel making th e depth-charge n ttack By direction of Office of Naval Operations this Study of "D th Ch Washington, October 1, 1918. will be nssumcrl to b e a cruiser of 15 knots speed and a turning circle of 600 ym·cls; her length is assumed to be Patrol Detachment, based on o. N. I. Publication No. 44, is iss~~d f arge :roblems," made in the American Naval Service. or the information of the United States 300 fect . The s ubm arines which m ay be expected in the wa tors co-.;-orwl b y th e detachment arc the large con ­ vcrted subm~rincs of the U-Dou tschln.nd type; it is assumed tlrn L their m aximum submerged s1wnd is 0 knots This pamphlet is most confidential and for the use of commissioned fii o cers only. and thn. t theu- Lurning circle submerged is 500 yar ds : tha t th oi.r length is 210 feet. d ROGER WELLES, Twnlve ty pical situn.tions wi.U be consi<lcrecl; the submarine w ill be assumc,cl to ·fi.re each of the four stnndnI" / Rear Admiral, United States Navy, shots in turn from firing positions bron cl on th e how, on the beam, a nd on tho quar tor of tho target -.;-csscl. Firing Director of Naval Intelligence. ~-angcs of 400 and 500 yn.rcls will b e used. In e11ch r.asc it will b e assum ed t.lrn t a submarine exposes i ts periscope rn a favornblo firing position; that the commander is able to fi re a torpedo n.t the t n.rget vessel on a correct course 00 at tl~e expiration of 15 seconds; tha t a t t his instim t h e lowor::i his p eriscope aga.in n.nd j,, abl0 to conuncr_i- m ukrng any ch ange of course and speed which seems m ost desirn.hl<': nothing furt,hnr is seen of tlw snhrnnrino for the dumtion of the problem- fi ve m inutes. It is assumed tha t the lookouts on the target vessel see tho periscope a t the ins tnn L when it is fi rst exposed: tha t the ship m ay comm ence u,ny m n.n euver at the expirntion of 15 scconch; - th at is, n.t t ho instmlt the tor pedo is fired from tho s ubm1trinc. rr h is ins tan t is considered as zero minu tes of th o problem nncl the timm; of flll ev-e.nts which occm· lrttcr nrn r eferred to i t . In all tho problems 11 n umber of courses are plotted for tho submar ine a nd t he ship. The course consider ed bes t is m arked : " First course for s ubmarine" or " F irst course for ship ." Tho second best com-so is marked "Second course for submar ine." T ho p ositions of the ship nr c plot ted a t h alf-minute intorvuls. D opth ch 11-r~es arc n.ss urned to be inv11riahly effective n.t a dis tance of 70 feet and cir,cles drawn with this distnnco as 11 r a clnis indicate the danger ar eas of 1111 depth ~h arges dropped . The figure inside the circle indicntcs the dep th at which the explosion occur,,, while the figures alongside tho circle indica te the timo in minutes tu1cl seconds after . tl:~ b eginning of the problem nt which the charge explodes. The p osition of tho subm11rino is plot.tod whoncvC'r it J::, wi th in several hundred yards of dep th-ch arge explosions. The 12 spncial cnscls will now b e cons iclerocl. 83619-1&---- I • 2 CASE I. DIRECT BOW SHOT FROM 500 YARDS ON THE BEAM. SUBMARINE. A direct bo\\· shot from about this position will _p robably be the most frequent of all torpedo shots. It is, however, only a m?der~tely good sho_t._ T he "track angle "-the angle between the course of the torpedo and the course of the sl11p- 1s a good one; it is about 75°, which is specially recommended by the German instructions. The r3:nge-500 yards-is rather great, as it allows the target ship about 34 seconds in which it can maneuver to avoid the torpedo. The submarine is moderately secure against depth charge counterattack. Ge1:man sub marine commanders have, according to their instructions, two courses of action open to them after firmg a torpedo: 1. To submerge immediately to 148 feet and run for 15 minutes. 2. To watch the results of the shot, observe the counter moves of the target vessel and then submerge 5/x,th Coarse /or.5'ab/77a..rz·ne to 148 feet for 15 minutes. If it can be assumed that the submarine commander can expose his periscope so skillfully that it can not be seen by the lookouts on the target ship- who will be specially alert after the torpedo has been sighted-then the second course of action has great advantages. If the target ship is missed and it turns to the right, a second torpedo can be fired, probably an angled stern shot. If the target vessel is seen to ttli'n to the left, then all the submarine has to do is to turn to the right, thus completely avoiding a depth charge attack. However, it seems that it would be extremely improbable for a submarine to repeatedly expose its periscope at 500 yards range ' without being sighted by a well-organized lookout system, such as that used in the vessels of the detachment. While, therefore, some extremel.v skillful commanders may observe the shot- for example, one submarine commander claims to have avoided 200 depth charges in· this way- it seems that the great majority would ~•second Course submerge immediately to 148 feet after firing at a man-of-war. While the speed of the submarine, while going : rorc.5'/Jt/) I to this depth, is not given in the German instructions, it would seem that their spirit implies that the submarine J rourr/1 Covr.fe Ship I gain this depth as <]Uickly as possible; therefore a high speed will probably be used. /orSuLJrnar/ne After the clepLh of 148 feet is reached, the submarine has, in general, two courses of action open to it: l. '1.'o nm at very slo"· speed .so as to keep within the turning circle of the target vessel. , f 2. To run at full speed so as to get outside the turning circle as soon as possible and to gain the , , ' , greatest start possible on the target ship before it can tmn around. , ; ~ , The first method may look excellent on paper; in actual practice it is, however, not so gootl.